1. Field of the Invention
The present invention relates to a machine tool, having a boring bar magazine which may incorporate boring bars, which may perform turning with the boring bar.
2. Description of the Related Art
Boring bars are categorized in terms of types into regular boring bar, of which a length is 4 to 5 times longer than a diameter, and long boring bar having a length longer than the length of the regular boring bar. A technology relating to a machine tool in which a boring bar is mounted on a tool rest to turn a workpiece is disclosed in Japanese Patent Application Laid-Open No. 2003-80408 and Japanese Patent Application Laid-Open No. 64-2839.
The machine tool disclosed in the Japanese Patent Application Laid-Open No. 2003-80408 is structured that the tool rest may be moved in any directions of axes X, Y and Z. Also, in this machine tool, two devices for transferring the boring bar, in which boring bars are laid on their tables respectively, are juxtaposed in the Y-axis direction.
However, the devices for transferring the boring bar are not moved in the Y-axis direction. For this reason, the tool rest has to be moved also in the Y-axis direction in addition to the X-axis and Z-axis directions. As a result, there is a problem that the machine tool as a whole is complicated because of the necessity of means for moving the tool rest in the Y-axis direction.
Also, because the devices for transferring the boring bar are juxtaposed in the Y-axis direction, there is also a problem that it is impossible to increase the number of the boring bars which may be incorporated therein.
Japanese Patent Application Laid-Open No. 64-2839 discloses a lathe having a tool stocking device (boring bar magazine) which may stock a plurality of tools (boring bars). This tool stocking device is adapted to stock the plurality of tools and to make a swivel motion and is mounted on a headstock.
However, a heat generating source such as a motor is located in the headstock. For this reason, there is a fear that the heat generated in the headstock would propagate to the tool stocking device so that the tools stocked in the tool stocking device might be thermally deformed. On the other hand, when the tool stocking device is operated during machining with the lathe, there is also a fear that a vibration of the tool stocking device would propagate to the headstock so that an adverse affect such as degradation in machining accuracy would occur.
Further, because the tool stocking device is located on the headstock, a motor, a pulley, a partitioning plate and the like of the headstock would obstruct. As a result, an operator could not perform the operating work or the maintenance work by extending his or her hands from a front side of the lathe. The load imposed to the operator is high.
In another known machine tool, a clamping and unclamping mechanism is used for clamping a tool holder of a boring bar to the tool rest. In this conventional clamping and unclamping mechanism, a clamping part having a predetermined shape such as a T-shape is interposed, and the clamping part is drawn by a piston or the like. Thus, the tool holder is indirectly drawn and clamped through the clamping part.
However, according to this prior art, because the clamping part is needed, a dimension from a center of the tool rest to a centerline of the tool holder is elongated. As a result, when a workpiece is turned by the boring bar, a moment due to a force applied to a machining position is increased. Accordingly, there is a problem that a large stress is applied to the position adjacent to the clamping and unclamping mechanism. Also, there is a tendency that the rigidity of the tool rest and the tool holder as a whole would be reduced.